Improvement in latch means for collapsing taps



July 12, 1955 R, M. STRICKLAND 2,712,658

IMPROVEMENT IN LATCH MEANS FOR COLLAPSING TAPS Filed Feb. 16, 1953 3 Sheets-Sheet l 11/ \&

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July 12, 1955 R, M. STRICKLAND 2,712,653

IMPROVEMENT IN LATCH MEANS FOR COLLAPSING TAPS Filed Feb. 16, 1953 3 Sheets-Sheet 2 Tlg E g 7% mw 12, 1955 R. M. STRICKLAND 2,712,658

IMPROVEMENT IN LATCH MEANS FOR COLLAPSING TAPS Filed Feb. 16, 1953 5 Sheets-Sheet 3 /2? A55 1 7 /?0 /50 /4 2D I g 1 //6 United States Patent 0 IMPRQVEMENT 1N LATCH MEANS FOR CGLLAPSING TAPS Royce M. Strickland, New Haven, Conn., assignor t0 Greenfield Tap and Die Corporation, Greenfield, Mass., a corporation of Massachusetts Application February 16, 1953, Serial No. 337,012

3 Claims. c1. 10-145 This invention relates generally to taps 0f the tapered thread-cutting type, and more particularly to power-operated and self-collapsing taps of this type.

A prior self-collapsing power tap of this type is shown and described in the patent to Breitenstein, N0. 2,135,067, dated November 1, 1938. for a plurality of tapered thread-cutting chasers which are radially moved into and from cutting engagement with work by means of cams on an axially movable operating plunger in the carrier. The operating plunger, which is normally spring-urged into a retired position in which the chasers are collapsed out of cutting engagement with work, is connected for joint axial movement with a latch that is normally yieldingly urged radially outwardly into locking engagement with the adjacent end face of a ring on the carrier when the plunger is advanced into its operating position in which the cams thereof hold the chasers in thread-cutting engagement with work. Axially slidable on the ring is a tripping member having an inclined surface which cooperates with a similar inclined surface on the latch to cam the latter radially inwardly out of locking engagement with the ring and release the operating plunger for springreturn to its retired position when the advance of the tripping member is stopped prior to the termination of the usual advance movement of the chasers into the axially immovable work. Provisions are also made in this prior tap to retract the chasers, prior to theconclusion of a thread-cutting operation, to such a slight extent that they will for the brief remainder of their threadcutting operation perform on the work with a relatively fine finish cut, and thus prevent the formation of highly objectionable shoulders on the thread when the chasers are suddenly retracted therefrom on spring-return of the operating plunger into its retired position. To this end, an outer portion of the locking surface of the latch is inclined to the adjacent end face of the ring so that the operating plunger will, during the inward camming of the latch out of locking engagement with the ring and prior to the release of the latch from the latter, be spring-returned from its normal operating position to such a slight extent as to bring about the aforementioned finish-cutting performance of the chasers for the brief remainder of their thread-cutting operation. Since for efficiency and other reasons only a small fraction of the time allotted for a thread-cutting operation of the chasers is reserved for their finish-cut performance, the latch is cammed out of locking engagement with the ring during a correspondingly small part of the normal advance motion of the chasers for a thread-cutting per formance, wherefore the locking surface of the latch is necessarily of small width radially of the ring, and its inclined portion is even of smaller width. It is this small width of the inclined portion of the locking surface of the latch which is responsible for occasional malfunctioning of the tap in the important respect of the finish-cut of the chasers toward the end of a thread-cutting operation. Thus, it happens occasionally with fairly new This prior tap has a carrier Fa'tented July 12, 1955 taps, and more frequently with older taps, that the narrow inclined portion of the locking surface of the latch jumps from interlock with the adjacent end face of the ring under conditions of disturbance such as even slight vibration or shock, aided and abetted by the tendency of the spring force on the operating plunger to draw the inclined surface portion of the latch out of locking engagement with the ring. This tendency of the latch to jump prematurely from interlock with the ring is even enhanced by an unduly limited contact area between the inclined surface portion of the latch and the adjacent end face of the ring. Thus, the latch has a partcircular periphery which fits in the ring and is drawn thereinto when the latch is released from interlock therewith and the operating plunger is spring-returned to its retired position. Accordingly, the inclined portion of the locking surface of the latch, which is formed by a bevelled outer edge of the latter, has only a line contact with the adjacent end face of the ring when riding on the same and, hence, offers little resistance to disturbing forces which tend to jump the latch from interlock with the ring. Moreover, the line contact between the bevelled edge of the latch and the adjacent end face of the ring results in early and excessive wear of a very small local; area of the latch which is the very area thereof that cooperates with the ring in controlling the slight spring-- return of the operating plunger from its normal operating; position for the achievement of the brief finish-cut per formance of the chasers toward the end of their thread-- Early and excessive Wear of the latch. at this critical contact area further enhances the chances cutting operation.

of malfunctioning of the tap and leaves much'desired'. in the way of accurate control over the brief finish-cut; performance of the chasers.

It is the primary aim and object of the present invention to provide a self-collapsing power tap of this type: which has none of the deficiences of the aforementionedi tap.

Thus, it is among the objects of the present invention to provide a tap of this type with a latch which will per-- form the same functions of locking the operating plunger in its operating position against spring-return into its retired position during the greater part of a thread-cutting operation of the chasers and permitting slight springreturn of the operating plunger toward the end of a thread-cutting operation for the brief finish-cut performance of the chasers, yet which will fail to jump from interlock with the ring under any circumstances and will show little wear even after long use.

It is another object of the present invention to interpose the latch as a connecting link between the opera ing plunger and an aligned spring-urged retract plunger in such wise that the latch is axially movable with the retract plunger and has a cam connection with the operating plunger for slightly retracting the latter from its normal operating position for a finish-cut performance of the chasers when the latch is cammed from interlock with the ring, permitting thereby a non-bevelled formation of the locking surface of the latch which affords a very substantial contact area between the latch and the adjacent end face of the ring with optimum locking performance throughout the cam-out of the latch from interlock with the ring, and consequently subjecting the locking surface of the latch to little wear and assuring secure interlock between latch and ring until the former is by cam action released from the latter.

It is a further object of the present invention to provide the cooperating cam faces of the aforementioned cam connection between the latch and operating plunger with considerable contact areas, thereby to reduce wear of these cam faces to a minimum and facilitate their formation, as well as obtain a most accurate control over their brieffinish-cut performance on the latter 'toward- Big. 3 is; a section taken on the line 3 3 of Fig. 2;

Figs. 4' and} are longitudinal: sectional-views, partly inelevation, of the tap in different operatingconditions ofthe same;

' Fig. 6 is a'longitudinal section through the tap in stillf another operating" condition of the same;

Fig. 7 is another longitudinal section through the tap,- takensubstantially-on the line 77-of-Fig. 4;

Figs. 8 and 9'a re cross-sections through the tap, taken' substantiallyon the lines 8+3 and 9 9', respectively,

of--Fig;- 4;

Fig; 10 is a longitudinal section through a part ofthe p? Fig. 11 is a cross-section through a part ofthe tap; showing aslightly modified version of the latter; and Fig. 1-2 is an enlarged fragmentary section through work which has'been threaded' with the present tap.

Refering to the drawings, and more particularly to Figs. 1 to 7 thereof, the reference numeral 2Q designates a self-collapsing power tap having acarrier22 which at its front is centrally recessed at Hand there provided with a plurality of 'equi-angularly spaced radial guideways 26, inthis; instance four, for .the reception of'chasers 28 forcutting tapered threads. The chasersZS are-held in their respective guideways 26 in the carrier 22 for axial movement with the latter bymeans of 'a'retainer dise39 Slidably interlocked with the inner ends of'the chasers 28 in the fashion shown in Figs; 2 and 3 are cams or wedges 32 on the forward end of an operating member orplunger 34 which is axially slidablein a central bore 36 in the carrier 22. Thus, the chasers-28j will be moved outwardly into cutting engagementwithwork W. on sliding the operating plunger 34in the. direc tion. ofthe arrow- 38 in Fig. 2, and the chasers will'bei moved inwardly out of cutting engagementwith the work I on sliding the plunger inthe opposite direction.

The carrier 22 iscylindrical and carries on its periphery an asially slidable sleeve 40 which through a transverse key 42 is operatively connected with a spring-urged plunger 44 in the central bore 36 in the carrier 22. The

key 42, which is releasably secured in the plunger 44- by thethreaded end 46 of a rod 4-3,; extends through an;

elongated slot 50 in the carrier 22 and is fittedlyreceived with its ends in diametrically opposite slots 52, respectively, in the sleeve 40 (Figs. 4, 5 and 7). sleeve4ll" may be considered a head ofthe spring urgedplnnger 44,- and' both, head and plunger, are held non-rotatable.

relative to the carrier 22 by the key 42; The plunger head 40-isintermedi ate its ends providedwith a pant-peripheral groove 54having a semi-cylindrical bottom 56 merging tangentially into diametrically opposite flats '58 in the plungenhead (Figs. 4, 5, 7 and 8'). Forni fitted'in the part-peripheral groove 54 in the plunger head ltl and guided-therein for radial movement is a lat ch '6 0; off openring shape (Figs. 4 and 8), having anend face.

62--Which,'during a thread-cutting operation of the chasers 28, is adapted to be in locking engagement with a stop shoulder 64 that is formed by the adjacent end face of the cylindrical rirn'66 of a cup element68 on the carrier 22; Compression-type springs 70, received in; sockets thelatch 60 andbearing against the cylindrical gttvat fijq hwar er he a ro ve mm;

head 40, normally urge the latch 64) into the locking position shown in Figs. 2 and 4 in which arelatively narrow marginal portion of its end face 62 is in locking engagement with a portion of the adjacent end face 64 of' the rim 66 of the cup element 68 on the carrier. The cup element 68 is threadedly received with its bottom 74 on the carrier 22 for axial adjustment thereon.

The earlier mentioned rod 48, which is threaded with one end into the plunger 44, extends rearwardly into an enlarged central bore 78 in a shank portion Si of the carrier 22 .(Figs, 1 and 6) and is surrounded by a com-- pression spring 82 which is interposedbetween a head 84 on the rod 48 and a washer 86 seated against an annular shoulder 88. in the carrier. The spring S2 normally urges the plunger 44 and its head 4t into the retract position shown in Fig. 6 in which the plunger head 40 rests against the bottom 74 of the cup element 63 on the carrier. The plunger head 40 assumes its retract position" when the Chasers 23 are retracted from work W (Fig. 6), as will be explained more fully hereinafter. On the other hand, the Chasers 28-will be in thread-cutting engagement with the Work Wwhen the plunger head 40 assumes the advance position shown in Fig. 4 in which the-latch 60-is locked to the stop shoulder 64 to prevent the spring-return of the plunger head into its retract position; during the thread-cutting operation of the chasers A coupling -9il, to be described more fully hereinafter, is provided between the latch 60 and the operating plunger 34 to connect them for jointaxial movement.-

The-plunger head 40 is received with a sliding fit in the rim 6560f the cup element 68 (Fig. 4), and the formfitting latch 60 must, for its release from the stop shoul der 64, be depressed into the part-peripheral groove 54 in theplunger head 40 to the extent indicated in Fig. 5 before the latch will permit the spring-return of the plunger head into its retract position (Fig. 6). Longitudinally slidableon the plunger head 40 and on the rim 66 of the cup element 68'is a sleeve 92which has a spline connection 94-with the plunger head 48 so as to be nonrotatable; thereon (Fig. 9.). The spline connection 94 comprises in thisinstance a key 96'on the plunger head 40 (Figs. 4and' 5), and a longitudinal groove 98 in the sleeve 92; (Fig.9) in which the key 96' is slidably' received. The sleeve-92- is provided with an internal frusto-conical cam surface l fltlwhich is adapted to cooperate with a similar; frusto-conical cam surface 102 of the latch 69 in-- carnming-the latter from its locking position (Fig. 4) into its. release position (Fig. 5) on relative axial movementof;

the-'plun'gerhead- 40 and sleeve 92,'as-wi1l be readily understood.

1 Whentherpresent tap '29 is'idle, the plunger-head 40 is normally in its retract position (Fig. 6) inwhich'the chasers-28 are fully retracted from work. To set the tap fora thread-cutting operation, the plunger head 40-is shifted; against theforce of its return spring 82, into the advance-position shown in Fig. 4 in which the latch 60 will automatically become locked to the stop shoulder 64 and the chas'ers lfi are projected outwardly for a. thread cutting-operation. To shift the plunger head 40 from its.-

retraot po sition into-its advance position, there is provided 3,:'I'SttlHg- 1e:YI'- or handle 104 which is pivoted in-the sleeve-92 and has a ball-shaped end- 106 received -in a socket-like opening 108 in'the carrierZZ (Figs. 2 and 6).-

More particularly, the resetting ha'ndielilihas an intermediate ball-shaped'portion 110 which is substantially fittedly received in an opening 112 in the sleeve 92'and" mounted on a pivot pin 114 in the latter. To reset the tap'for a thread-cutting operation, the handle 104 is turned counterclockwise from the idle position in Fig; 6 into thereset position in Fig. 4, moving thereby the sleeve 92 aigially forwardly relative to the carrier 22. Since the sleeve 92;bears normally against an annular shoulder 1161 at n unsq h as 6 (H s it t n 10 9 592 a $97919 grihs d. s a so moved: f r a d y y he have;

92 when the handle 104 is turned to its reset position (Fig. 4) in which the plunger head is sufiiciently advanced to permit the latch 60 to snap into locking engagement with the stop shoulder 64.

Usually, a tap of this type is axially moved with its chasers into the work W to be threaded and the work is turned during the thread-cutting operation, although it is apparent that either the tap or the work may be rotated as well as moved axially, or the tap may be rotated and the work moved axially, for a thread-cutting operation. For its usual axial movement for a thread-cutting operation, the tap 28 is mounted with the shank portion 80 of its carrier 22 in the turret 118 of a screw machine or in any other suitable holder. For a thread-cutting operation on work W, the tap 20 is reset, as described, by means of the handle 104 while the chasers 28 are outside the work. Thereupon, the tap is advanced with its chasers 28 into the rotating work, and the chasers will start to cut a thread substantially when the tap reaches in its forward travel the position shown in Fig. 4. The chasers 28 will during the continued forward travel of the tap from the position in Fig. 4 cut more and more of the tapered thread t in the work, as will be readily understood. Somewhat prior to the conclusion of a threadcutting operation of the chasers 28, the front face 120 of the sleeve 92 moves into engagement with any suitable fixed stop 122 and is held axially immovable thereby while the carrier 22 and the plunger head 49 with its latch 68 continue to move forwardly for the brief remainder of the thread-cutting operation. It is during this brief continued forward travel of these parts relative to the stopped sleeve 92 that the cam surface 100 of the latter cooperates with the cam surface 102 of the latch 60 in carnming the latter from locking engagement with the stop shoulder 64 (Fig. 5) and permitting spring-return of the plunger head 48 into its retract position (Fig. 6) for full retraction of the chasers 28 from the finished thread I in the work prior to the axial retraction of the tap from the work.

To limit rearward movement of the sleeve 92 on the plunger head 48 and cup element 68 so that the ball end 166 of the resetting handle 104 will in no event be turned out of register with the socket-like opening 108 in the carrier 22, the sleeve 92 receives a stud 126 (Fig. having a shank 128 which projects into a longitudinal groove 13%? in the plunger head 40. The effective travel range of the shank 128 in the groove 130 may be regulated by an adjustment screw 132 in the plunger head 49. The screw 132 is readily accessible for adjustment purposes through aligned holes 134 and 136 in the cup element 68 and plunger head 40, respectively. The sleeve 92 is also provided with a peripheral groove 138 for use with a shifter fork for tap-resetting purposes, in which case the resetting handle 104 may be removed from the tap and a filler plug 14f) mounted in the opening 112 in the sleeve 82 by means of the same pin 114 which serves as a pivot pin for the resetting handle 134 (Fig. 11).

The previously mentioned coupling 90 comprises a transverse key 142 (Fig. 7) which is releasably retained in the operating plunger 34 by the conical tip of a springurged plunger 144 and extends through and beyond the elongated slot 50 in the carrier 22 and aligned slots 146 in the plunger head 40. The opposite follower ends 148 of the key 142 extend into opposite cam slots 150, respectively, in the latch 60 (Figs. 4, 5 and 7). The cam slots 150 are inclined to the longitudinal axis of the carrier 22, wherefore these cam slots will, during the radial cam-out of the latch 64 from locking engagement with the stop shoulder 64, cooperate with the follower ends 148 of the key 142 in slightly retracting the operating plunger 34 from the chasers 28. Such slight retraction of the operating plunger 34 during the cam-out of the latch 60 from locking engagement with the stop shoulder 64 will result in slight retraction of the chasers 28 from the work to such a desired extent that the chasers will during the brief remainder of their thread-cutting operation perform with an increasingly finer cut on the work and thereby avoid the formation of highly objectionable shoulders s on the thread t (Fig. 12) which would be formed if the chasers would at the end of their thread-cutting operation be suddenly retracted from the work without previously changing their cut from normal to finer. Of course, the chasers 28 will be conditioned for their normal-cut performance when the tap is, after retraction from the threaded work, reset for the next thread-cutting operation (Figs. 2 and 4). Thus, the coupling serves not only to impart the axial motion of the plunger head 40 and its latch 60 to the operating plunger 34, but serves also to achieve a change in cut of the chasers on the work from normal to finer at the end of their thread-cutting operation to prevent the formation of highly objectionable shoulders on the finished thread.

The non-bevelled formation of the locking surface 62 of the latch 60 in a plane at right angles to the axis of the tap affords a maximum contact area between the latch and the stop shoulder 64 with optimum locking performance throughout the cam-out of the latch from locking engagement with the stop shoulder, subjects the locking surface of the latch and the stop shoulder to only negligible wear over a long period of use, and assuredly prevents jumping of the latch from locking engagement with the stop shoulder under all circumstances. Further, the follower ends 148 of the key 142 are preferably provided with opposite cam surfaces 152 of considerable surface area which are in uniform engagement with the inclined sides 154 of their receiving cam slots in the latch 60 (Figs. 4 and 5). Also, the cam slots 150 in the latch 60 and the follower ends 148 of the key 142 may be made of considerable width for adequate strength of the key as a safe motion transmitter between latch and operating plunger. Of course, the considerable dimensions of the cam slots 150 in the latch and of the follower ends 148 of the motion-transmitting key 142 facilitate the accurate machining of these parts, reduce wear of the cam slots and registering follower ends of the key to a minimum, and afiord a most accurate control over the slight retraction of the chasers from the work for their brief finish-cut performance on the latter toward the end of a thread-cutting operation.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning of equivalency range of the appended claims are intended to be embraced therein.

What is claimed is:

1. In a collapsible tap having a centrally recessed and longitudinally slotted carrier provided with an external stop shoulder and substantially radial guideways for a plurality of chasers, and an operating member axially movable in said carrier recess for moving said chasers, the combination of a spring-urged plunger movable axially of said carrier and having a longitudinally slotted head slidable on the outer periphery of said carrier and provided with an outer peripheral groove; an open-ring latch received in said peripheral groove in the plunger head and guided therein for radial movement; a coupling between said latch and member for their joint axial movement, said latch being normally yieldingly urged radially into locking engagement with said shoulder to hold said plunger against spring-return from an advance position into a retract position in which said member holds said chasers in and out of cutting engagement with work, respectively; and means for depressing said latch radially out of locking engagement with said shoulder, said coupling being formed by a transverse key in said member extending through said slots in said carrier and plunger head and having opposite follower ends, and opposite cam 95s; ia aid; Qpa i a atcl r seiy nas id f l owa r da mq y lyi nd. co pe atin h r wi h, den fis q p aid atch; out-. 2 pskr a e a qm m th aid: hp slen.

mq esaidm mh r; x ally i sli ht e r et q l a d, 2 a r qia; QQIIILQL q 9; afinar. 1. 1 9.1L wq k.

- .The mbiaa qain a Q lag hleap. s t fiqrth. Q1 2 1. a d m lot a a d. filxr na a h. e s rai htr l t aqli pd ta qarx er; ati s, arid sa d QllQWQ e ds fisaid, y ha mila ly clined opposi e aces; n. vnifprm. on ag mpm; th he lls: o a

clia dzsl ts- 7' r 3-. n a q lapsible-t n h y n aaant ally 1ZQSQ an n itud na l l tt d c rrie p qy ds dr w th s bst nt a ad al uidew y pl: s' l ra ityw ha ra 1 1? l -r meat: 031; sa d; art e a n q hdri a ia p c d;

tward ma e; atter; nd n pv s sdv h n 11 face which Serves as raopr sl ld rr a d 1. perat n member meyahle. n, a d. qatn e i= q o ma nasaid h se s he pmb natiqnr o a w llau as .v phm mg ble axiall Q aid ards; nd, hav n id ylin r cald 21 a d man er; h a ha ng r t m V diate arls: iametri all Qp qsit fl and Pa p riphera z rq ve; h nds; xi-t e. c m f h h e forgled by said flats; an open ring lateh form-fitting i1; saidrpa tene phw ra r v a p r h nd. guided thereir ifor radial movement; acdupling between said; latch; and member for their joint axialmovement,

'gagement with Work, respectively; and means for de-' 8 saidalatgh beipg normally yieldingly urged radially outward into locki g engagen e t with said stop shoulder to hold sai plur ge; against spring-return from an advance p'os'itiofi' into a retract positiori' in which said 7 member holds said Chasers. in and out of cutting enpressing said latch; radially inwardly out'o'f locking engagcrneiit with said stog shoulder and into form-fitting relation with said part-peripheral groove to permit springretrirn of said pluhg erfinto its, retract position in which said latch is within. said cylindrical rim of said cup element; said cougliiigi beiirigformed bya transverse key in said member extendirig through said slots in said carrier andlhgger head. and having opposite follower ;ends, and opposite cam slots in said open-ring latch References Cited in the file: of this patent UNITED STATESPA E TS 909,749 Brown Jan. 12, 1909 1,782,804 Breitenstein- Nov. 25, 1930 2,135,067. Breitenstein Nov. 1, 1938 

